Unit 8 - Types of Waves (focus: mechanical waves)

Unit 8 - Types of Waves

(focus: Mechanical waves)​

I know...

• how to determine if a wave is transverse or longitudinal.

Learning Target​

I can...

• compare the pitch of 2 waves when given their waves description/image.

​​Success Criteria​

Wave Recap​

Multiple Choice

Waves can carry _____.

• matter

• air

• energy

• space

Multiple Choice

True or False: Electromagnetic waves need to have a medium to travel.

• True; they cannot travel without a medium

• False; they can travel through space (vacuum)

Electromagnetic waves

Mechanical Waves

Surface waves

​3 types OF WAVES

surface WAVES​

these are waves that travel along the surface between two mediums. (combination of both transverse and longitudinal waves)

• Example:

  • an ocean wave because it travels at the surface between water (liquid) and air​​ (gas)

• Examples:

  • solids (land), liquids (the ocean), and gases (air)​

mECHANICAL WAVES​

• type of wave that needs matter (or medium) to transfer energy

  • A medium is the substance through

    which a wave can travel.

​​Types of Mechanical Waves​

Transverse Waves

• Energy causes the matter in the medium to move up and down or back and forth at right angles to the direction the wave is traveling; perpendicular.

  • Examples: ocean waves

Parts of a Transverse Wave

Crest

• ​the highest point on a wave.

Parts of a Transverse Wave

Trough

• ​the valley (lowest point) between two waves

Parts of a Transverse Wave

Wavelength (λ)

• ​the horizontal distance, either between two crests or troughs of two consecutive waves.

Multiple Choice

What part of the transverse wave is shown by number 1?

• crest

• trough

• wavelength

• amplitude

Multiple Choice

What part of the transverse wave is shown by number 2?

• crest

• trough

• wavelength

• amplitude

What is frequency?

​Remember that frequency (f) is the total number of waves over a given amount of time

• The greater the number of waves per second:

  • the higher the frequency

  • the more energy the wave carries

​HIGH

​LOW

What is frequency?

​High frequency sounds have a high pitch.

• so the closer the waves are, the higher the frequency and pitch​

​HIGH

​LOW

Parts of a Transverse Wave

Amplitude

• the peak (greatest) value

  (either positive or negative) of a wave. The distance from the undisturbed level to the trough or crest.

(think of it like the height of a wave)

Parts of a Transverse Wave

Amplitude

• the height of a wave gets larger as the amount of energy in the wave increases.

  • larger amplitude = LOUDER sound and more ENERGY

Multiple Choice

Which transverse wave has the higher amplitude?

• Wave A

• Wave B

​​Types of Mechanical Waves​

Longitudinal (compressional )Waves

• wave in which matter in the medium moves forward and backward along the same direction that the wave travels.

  • Examples: Sound Waves; springs

    • A sound wave is a compression wave that has compressions and rarefactions, which travels through a medium

Parts of a compressional Wave

Compression

• the part of the wave where the particles are crowded together.

Parts of a compressional Wave

Rarefaction

• the part of the wave where the particles are spread apart.

What about amplitude?

Amplitude increases when particles in compressions are more compact and particles in the rarefactions are more spread out.​​​

LOW AMP​

​HIGH AMP

​REMEMBER

Higher Amplitude = More Energy​

Multiple Choice

Which compression wave has the higher amplitude?

• Wave A

• Wave B

what are the mediums?

• Sound can travel through solids, liquids, gases​

​​Sound waves travel fastest in solids and slowest in gases. This is because particles in a solid tend to be closer together (more dense).

What does that Mean?

Generally, the speed of sound will increase as the density of the material increases.

​Material	​Density	​Speed
​Air	​0.00139	​331.5
​Water	​1.00	​1496
​Skull bone	​1.91	​4080
​Glass	​2.23	4540
​Steel	​7.86	​5940

The Doppler effect

What is the Doppler effect?

it is a change in sound frequency that is caused by the motion of the sound source, the observer (the one listening), or both.​

• As a source of sound approaches, a person (the observer) hears a higher frequency (and pitch). 

•  When the sound source moves away, the person (observer) hears a lower frequency.

Multiple Choice

Do sirens have a higher pitch when they are farther away from you or closer to you?

• farther away

• closer to you

Multiple Choice

In the image, which person will hear the siren at a higher pitch? Why?

• the girl, because the wave frequency is higher going away

• the girl, because the wave frequency is lower going away

• the guy, because the wave frequency is lower as it is approaching

• the guy, because the wave frequency is higher as it is approaching